海绵，丰富的生命过程 Sponge, a rich process of life

海绵是原始的多细胞生物之一，它们没有真正的组织器官，也没有神经系统和肌肉系统。但是，它们却有着丰富而神奇的生命过程，让我们一起来了解一下吧！

Sponges are one of the most primitive multicellular lifes, they have no true tissues or organs, no nervous system or muscle system. But they have rich and amazing life processes, let's learn about them together!

领鞭毛虫是一种微小的单细胞生物，其结构与海绵中的领细胞（也称领鞭毛细胞）非常相似。这些特化的细胞在海绵体内起着捕捉食物和生成水流的作用。科学家通过研究这些领细胞并分析其分子特征，提出了一个重要的假设：海绵可能是动物家族树上最早分支出来的动物。

Choanoflagellates are tiny, single-celled creatures that look very similar to a type of cell found in sponges called choanocytes. These special cells help sponges capture food and create water currents. Scientists have studied these cells and compared them to choanoflagellates, along with analyzing molecules in cells, to suggest that sponges are the first animals to branch off from the rest of the animal family tree.

那海绵是如何消化吸收食物的呢？

Well, how do sponges digest and absorb food?

海绵体内有许多小孔，这些小孔可以让水流进入中央腔。水流带来了微小的有机颗粒、浮游生物等食物。这些食物被海绵体壁上的鞭毛细胞捕获，并通过胞饮或者原生质流动送到其他细胞进行消化。消化后的营养物质可以在不同细胞之间传递，供给海绵生长所需。 

Sponges have many pores, these pores allow water to flow into the central cavity. The water brings tiny organic particles, plankton and other food. These foods are captured by flagellated cells on the sponge wall, and sent to other cells for digestion by endocytosis or protoplasmic flow. The digested nutrients can be transferred between different cells to provide for sponge growth.

海绵有一些独特的繁殖方式。它们既可以进行无性繁殖，也可以进行有性繁殖。

Sponges have some pretty unique ways of reproducing. They can do it both asexually and sexually!

那海绵具体是如何繁殖和生长发育的呢？

How do sponges reproduce and grow? 

上文说到，海绵有无性和有性两种繁殖方式。无性繁殖主要有出芽和形成芽球两种。出芽是由海绵体壁向外突出形成芽体，与母体脱离后长成新个体，或者不脱离母体形成群体。形成芽球是由中胶层中的原始细胞聚集并包裹几丁质膜和骨针而形成的。当环境恶化时，成体死亡后，芽球可以幸存并发育成小海绵

Sponges have two modes of reproduction: asexual and sexual. Asexual reproduction mainly includes budding and gemmule formation. Budding is when a part of the sponge wall protrudes outward to form a bud, which grows into a new individual after separating from the parent, or forms a colony without separating from the parent. Gemmule formation is when primitive cells in the mesohyl aggregate and wrap around chitin membrane and spicules.. When the environment deteriorates, after adult death, gemmules can survive and develop into small sponges.

在有性生殖中，大多数物种会将精子释放到水中，使卵受精。一些物种会将卵释放到水中，而另一些则会将卵留在体内。受精卵会发育成幼体，然后游到新的生活场所定居下来。

In sexual reproduction, most species release sperm cells into the water to fertilize the eggs. Some species release their eggs into the water, while others keep them inside their bodies. The fertilized eggs develop into larvae, which swim off to find a place to settle down.

海绵还以其能够从身体碎片中再生而闻名。但是，这仅在碎片包含再生所需类型的细胞时才起作用。一些物种通过出芽生殖，即新的海绵从母体海绵上的小隆起中生长出来。

Sponges are also famous for being able to regenerate from fragments that break off. However, this only works if the fragments contain the right types of cells. Some species reproduce by budding, which means that a new sponge grows out of a small bump on the parent sponge.

当海绵的生存条件变得不利，例如气温下降时，许多淡水物种和一些海洋物种会产生被称为“芽球”的“生存舱”。这些胞囊由未分化的细胞组成，保持休眠状态，直到环境变得更好。

When conditions become unfavorable for sponges, such as when temperatures drop, many freshwater species and some marine ones produce "survival pods" called gemmules. These are made up of unspecialized cells that remain dormant until conditions improve. 

然后，它们会形成全新的海绵或重新占据先辈留下的骨骼，等待更好的时机到来。

Then, they either form completely new sponges or recolonize the skeletons of their parents. It's like the sponges are waiting for better times to come!

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